The old conventional wisdom: Businessman John Brunner was running away with the GOP Senate nomination.

The new thinking: He still could win it, but the race is tightening.

The new threat to Brunner appears to be St. Louis area congressman Todd Akin, whom many Republicans had written off.

And, GOP insiders say, former state treasurer Sarah Steelman is not out of it.

In a remarkable irony, Kansas City, which Republicans have largely ignored, may wind up playing a crucial role.

Insiders say Brunner led by a wide margin when he was the only candidate advertising on TV. But that changed once Akin and Steelman launched their own ads.

Brunner ranks on many lists as the candidate Democratic incumbent Claire McCaskill would least like to face because he’s never held public office before and therefore has no voting record. That makes him an elusive target.

He has been the focus of ads sponsored by a political committee aligned with Steelman — and funded in part by rich guy Rex Sinquefield — and another one aligned with Democrats. These days, Brunner is getting pounded.

Akin now is the target of not one but two negative ads from Brunner — a sign that Brunner is wary of the man he describes as his friend.

Brunner shapes up as the lone candidate who lacks a geographic base. Akin, a six-term congressman, is said to be corralling the St. Louis area. Steelman is strong in the southwest.

For weeks, Brunner has been the only candidate advertising in KC, which may give him an edge here. That could be helpful given just how close this race is now said to be.

But Brunner faces a problem that often faces deep-pocketed political newcomers. While it’s easy to drive up name ID, that often fails to translate to votes because voters simply don’t know him. Support can fade.

Republicans and Democrats appear to agree on another point: Akin is the candidate McCaskill would prefer. He’s an incumbent congressman with six terms under his belt and a lengthy voting record, which gives McCaskill something to shoot at.

And he’s conservative.

Real

conservative. So conservative, in fact, that Democrats think that would give McCaskill a fighting chance in a year in which almost everybody says she’s battling from behind.

That McCaskill herself prefers Akin might be gleaned from a set of three ads her campaign just sponsored against each of her opponents. The Brunner and Steelman spots hit hard.

The Akin ad? He’s depicted as “the most conservative congressman in Missouri,” “a crusader against bigger government” and carrying a “pro-family agenda.”

Portraying a Republican that way amounts to a pro-Akin ad in a GOP primary.